Image sensors using pinned photodiode pixels, typically implemented in CMOS architecture, are well known. Such image sensors in many applications have the advantage that both the image sensitive element and the image processing circuitry can be embodied in a single chip which can be manufactured using CMOS techniques.
However, there is increasing demand for image sensors for use in mobile applications such as mobile phones where power supplies are very limited. Specifically, as discussed in more detail below, many mobile devices have a battery supply at 2.4V whereas prior art pinned photodiode image sensors require a voltage of about 3V. This can be met by providing a charge pump, but at the expense of increasing the circuit complexity and cost. Moreover, the charge pump will typically require a storage capacitor which is too large to be provided on-chip, and thus an off-chip component is required.